Generally, when floor sheets are bonded to a base sheet of floor, in order to bind a seam of individual floor sheets tightly, a method of pouring a heat melted welding rod into the said seam is used. In this case, since the floor sheets are laid so closely each other from the beginning, it is difficult to press directly the heat melted welding rod into the narrow gap, which exists at the seam, from the top of the seam. Therefore, even if the welding rod had been pressed into the gap, the heat melted welding rod merely becomes firm on the surface of the seam in a state of being raised (See, FIG. 1). If this raised area is simply whittled away to flat the floor surface, the original seam appears again and the floor surface just returns to the original state. Therefore, it is practically impossible to bind each floor sheet tightly by using such method.
Generally, a U-shaped or V-shaped groove is cut at the seam part by using a hand cutter or the like (See, FIGS. 2 and 3), then the heat melted welding rod is poured into the groove (See, FIG. 4), and the raised area on the surface is whittled away to finish the surface flatly (See, FIG. 5). According to this method, except when it is difficult to cut a groove having desired depth since sheets are thin or hard, it is possible to bind sheets tightly to some extent.
In either case, it is required that the concave groove is formed uniformly along a seam without being displaced to right or left from a center of the seam by means of the above groove-cutting work. Therefore, in order for the seam to be placed at the center of a U-shaped or V-shaped blade of cutter, a ruler is usually set parallel to the seam, and the groove is cut contacting the blade of cutter with the ruler. With regard to this method, if the seam is short in length, it does not take time or care to work so much. However, when a floor space is larger and a seam is longer in length, there is a disadvantage that it takes an immense amount of time and effort and also an operating cost becomes huge.
In order that the groove can be cut easily on the seam of sheets, a grooving tool having a guiding function is proposed (for instance, Patent document 1). By using this tool, a relatively stable operation can be performed due to a support structure having a two contact points consisting of a blade edge and a guiding roller against sheet surfaces. However, since the distance between the support points and a grip is long, there are disadvantages that not only the stability is limited but also a tool itself is easy to break.
In addition, a floor grooving device equipped with rollers having a function for a guiding seam, at the front end portion and the rear end portion of the device itself is proposed (Patent document 2). With regard to this device, there was a disadvantage that this device causes a risk to cut off the part other than the seam of the floor in the process of operation, since the front roller, which is the seam guide, is apt to run off from the seam. Furthermore, there were other disadvantages that the device cannot follow the seam sufficiently, since the rear roller, even though a width of it is wider than that of the above front roller, is not always stable in the wide cut groove which is formed by a blade equipped just behind the roller provided at front of the device, and also the device cannot sufficiently correspond to surface irregularities of floor. And also, there was one more disadvantage that, the rear roller, and if the second blade is provided at the rear, the second blade should also be detached when a curved groove is formed, which is a troublesome operation.